Liquid photoelectrostatic developer unit



Feb. 10, 1970 w. MALONEY 3,494,328

LIQUID PHOTOELECTROSTATIC DEVELOPER UNIT Filed Sept. l, 196.6

POWER .5I/PPL Y The rrom/S Ys United States Patent OJ 3,494,328 LIQUIDPHOTOELECTROSTATIC DEVELOPER UNIT William Maloney, Lake Forest, lll.,assignor to Addressograph-Mulligraph Corporation, Mount Prospect, Ill.,a corporation of Illinois Filed Sept. 1, 1966, Ser. No. 576,612 Int. Cl.B05b 5/02 U.S. Cl. 118-637 9 Claims ABSTRACT OF THE DISCLOSURE A tonerlevel control for a liquid photoelectrostatic developer unit includes alamp and a photocell disposed opposite a light transmitting portion of apump conduit coupled to a developer tank. Changes in the toner levelcontrol the photocell to actuate a pulse generator which periodicallyoperates a toner dispenser to repeatedly add measured increments oftoner to the developer liquid until the proper toner level is reached. Atime delay circuit prevents operation of the toner dispenser until thepump has been operating for a period of time.

This invention relates to a liquid developer unit for photoelectrostaticcopying machines and, more particularly, to such a unit including meansfor automatically maintaining the liquid developer at a desiredcomposition.

Photoelectrostatic copiers using liquid developer units are generally ofthe type in which the developer liquid is pumped from a reservoir to anapplicator structure, such as a tank having sheet or web guiding means,in which the developer liquid is placed in contact with the surface ofthe web or sheet material bearing a latent electrostatic image to bedeveloped. The liquid generally comprises a liquid carrier containingelectroscopic developer or toner powder that is deposited on the sheetor web material in accordance with the charge image. These developerunits frequently include agitating means to insure uniform developerliquid composition or uniform distribution of the powder or toner in theliquid carrier.

Because of the removal of the developer powder by the sheet or webmaterial, it is necessary to replace or replenish the developer powderfrom time to time depending on the extent of use of the copier and otherfactors. The amount of powder in the developer liquid can be maintainedat the desired level by periodically adding either the developer powderor a developer concentrate including a rich mixture of powder and liquidcarrier. The developer liquid can also be maintained at the desiredcomposition by periodically changing the supply of developer liquid.These arrangements are not satisfactory because of the expense ofreplacing the developer liquid, the time required, and the danger that alow powder or toner level frequently cannot be observed before copyquality starts to deteriorate. Arrangements have been made to providemeans for automatically adding developer liquid or concentrate atperiodic intervals or on demand, but these arrangements frequently arenot capable of adding carefully controlled quantities or are such thatthe added liquid is not of uniform consistency. One improved arrangementfor dispensing toner or developer concentrate is shown and described indetail in the contemporaneously filed application of Robert F. Zawiski,Ser. No. 576,613, which application is assigned to the same assignee asthe present invention.

Although this application provides means for metering controlledquantities of developer concentrate of uniform consistency, it isnecessary to provide means for adequately measuring the ratio of powderor toner to carrier or the quantity of toner available in the carrierfor deposition on the sheets to be developed. In addition, thearrangement for measuring toner concentration must be such as to avoid aspurious reading resulting from measuring improperly mixed developerliquid or developer liquid from which the toner has been permitted tosettle out due to inactivity of the copying apparatus.

Accordingly, one object of the present invention is to provide a new andimproved liquid developer unit.

Another object is to provide a liquid developer unit including new andimproved means for measuring or detecting the quantity of developermaterial or powder in a liquid developer.

Another object is to provide means for automatically adding developermaterial to a developer liquid in accordance with the amount ofdeveloper material in the developer liquid.

A further object is to provide an arrangement for measuring the amountof developer material in the developer liquid that avoids spuriousreadings resulting from inadequate mixing of the developer liquid orsettling of the developer material from the liquid carrier.

In accordance with these and many other objects, an embodiment of theinvention comprises a liquid developer unit including a developerapplicator structure for receiving material to be developed, a reservoircontaining a quantity of developer liquid, and a pumping means forcirculating the developer liquid between the reservoir and theapplicator structure and for also circulating the developer liquid toinsure consistency of the mixture or a uniform composition thereof. Adeveloper concentrate dispensing assembly is also provided for addingcontrolled quantities of liquid developer rich in developer material tothe developer liquid in the unit to replace the developer material lostin the image developing process.

The developer concentrate `dispensing assembly is actuated by anelectric solenoid which, in accordance with the present invention, isconnected to a lirst control or bistable circuit which when placed inoperation alternately operates and releases the solenoid. Each cyclicoperation and release of the solenoid dispenses a predetermined amountof `developer concentrate into a reservoir `of liquid developer.

To provide means for controlling the operability of the bistable circuitfor operating the solenoid and dispensing assembly, a further controlcircuit or assembly is provided including an electric lamp orilluminating source and a light responsive means or photocell. These twoelements are spaced apart from each other to permit a portion of thedeveloper liquid to be disposed therebetween. These two elements thuscan be immersed in the reservoir or can be disposed adjacent a lighttransmitting portion of a fluid conveying means in the liquid developerunit, for example, a discharge line from the pump. The developermaterial or toner powder is substantially opaque and thus theconcentration of developer material changes the light reflecting andtransmitting characteristic of the developer liquid so that the lightresponsive means provides an output signal varying in accordance withvariations in the concentration of the developer material in thedeveloper liquid.

The light responsive means is connected to a switching means, such as atransistor, which selectively controls the application of potential tothe circuit for periodically operating the dispensing solenoid.Therefore, when the level of developer material in the developer liquidfalls below a desired level, the change in the illumination of the lightresponsive means renders the bistable circuit effective tointermittently operate and release the solenoid in the concentratedispensing assembly. This assembly adds increments of developer materialor concentrate to the reservoir until the desired ratio of developermaterial to carrier liquid is reached. At this time, the lightresponsive means renders the control circuit for the solenoidineffective.

The pumping means in the liquid developer unit not only serves to conveythe developer liquid to the point of application to the sheet or webmaterial but also serves to agitate the developer liquid in thedeveloper unit to maintain uniform consistency. This pumping means isoperated only during the intervals at which the copying machine is inuse. Thus, during periods of inactivity, the developer material tends tosettle out of the carrier liquid. Accordingly, there is a tendency forthe detecting unit including the light responsive means to indicate theneed for developer material when the machine is first placed inoperation and before the pumping means has operated a sufficient time toobtain a uniform dispersion of developer material in the carrier liquid.Accordingly, the control circuit of the present invention includesmeans, such as a time delay means, for inhibiting the operation of thedispensing unit until the developer liquid has been sufficientlyagitated by the pumping means to attain readings accurately reflectingthe ratio f developer material to the carrier liquid.

Many other objects and advantages of the present invention will becomeapparent from considering the following detailed description inconjunction with the drawing which comprises a schematic illustration ofa liquid developer shown in conjunction with a schematic circuit diagramof a control means therefor embodying the present invention.

Referring now more specifically to the drawing, therein is illustrated acontrol circuit for automatically monitoring the amount of developermaterial in a developer liquid and for controlling the automaticaddition of developer material by a dispensing assembly 12 to a liquiddeveloper indicated generally as 14. The control circuit 10 accuratelymeasures the ratio of developer material to the carrier liquid or thequantity of developer material available for deposition on the copies tobe reproduced and controls the dispensing assembly 12 to supply only thequantity of developer material to the developer unit 14 that is requiredto provide copies that are neither undertoned nor overtoned.

Although the construction of the liquid developer unit 14 can be of anyof the well-known constructions, it preferably comprises a liquiddeveloper unit of the type shown in the above-identified application ofRobert F. Zawiski. In general, this developer unit includes a tank orreservoir 16 adapted to contain a body of developer liquid 18. Thereservoir 16 is placed in communication with an inlet to a pumping meansor pump 20 through an inlet line 22, and an outlet line 24 from the pump20 is connected to an applicator structure indicated generally as 26which includes sheet or web guiding means and means for distributingdeveloper liquid over the surface of the sheet or web material bearing alatent electrostatic image to be developed. When the pump 20 is placedin operation, developer liquid from the reservoir 16 is drawn throughthe inlet line 22 and is discharged through the outlet line 24 to beapplied to the sheet material by the applicator structure 26, thesurplus of the liquid falling back into the reservoir 16. Thiscirculation of the developer liquid 18 thoroughly mixes and agitates thefluid 18 so that it is of uniform consistency in which the developermaterial or toner is thoroughly dispersed in the carrier liquid.

The automatic dispensing or metering assembly 12 is provided for addingtoner or developer material to the developer liquid 18 in the reservoir16 to replace the toner removed from the developer liquid during thedeveloping operation. This assembly 12 can comprise any suitableconstruction, but preferably comprises the construction shown anddescribed in detail in the contemporaneously filed application of RobertF. Zawiski, identiiied above. In general, the dispensing assembly 12includes a bottle or recep-tacle containing a quantity of developerconcentrate in which the ratio of developer material or toner to theliquid carrier is relatively high. This supply receptacle, which iscontinuously oscillated during the operation of the machine to maintainuniform dispersion of the toner and the carrier, is mounted at anelevation above the reservoir on tank 16 and includes a meteringassembly for discharging a known quantity of the concentrate through aconveying means 30 to the body of the developer liquid 18 in thereservoir 16. In one assembly 12 constructed in accordance with theinvention disclosed and claimed in the Zawiski application, eachactuation of the metering assembly discharges one milliliter ofdeveloper concentrate to the reservoir 16. This metering assembly in theassembly 12 is actuated by a solenoid 32.

The metering or dispensing assembly 12 discharges the fixed quantity oftoner concentrate through the conveying means 30 to the reservoir 16each time that the solenoid 32 is energized and released, as describedin detail in the above-identified Zawiski application. The energizationof the solenoid 32 is controlled by a relay 34 having a winding 34A anda pair of normally open contacts 34B. When the relay 34 is operated toclose the contacts 34B, the winding of the solenoid 3-2 is connectedacross one input of a power supply circuit 36 in series with a timedelay device 38. The time delay device 38 provides a control forinsuring that the dispensing assembly 12 cannot be operated when theliquid developer unit is started until the developer liquid 18 has beenthoroughly mixed and agitated to provide a representative sample forevaluation by the control circuit 10.

More specifically, when the copying machine of which the liquiddeveloper unit 14 forms a part is placed in operation, suitable controlmeans, such as a normally open switch 40, is closed to energize thepower supply circuit 36 and to start operation of the pump 20. Theoperation of the pump circulates the developer liquid 18 through theunit 14 and agitates and mixes the developer liquid 18 so that itattains uniform consistency. When the switch 40 is closed, a filament inthe delay device 38 is energized to initiate the timing period of thedevice 38. After a suitable delay, such as ninety seconds the solenoid32 can 'be operated and released under the control of the relay 34.

The control circuit 10 includes means for alternately operating andreleasing the relay 34 so long as the developer liquid 18 contains aninsufficient quantity of toner or developer material. The circuit 10exercises this control by examining the light transmitting or reflectingcharacteristic of a representative sample of the developer liquid 18. Toaccomplish this, the control circuit 10 includes a light source orilluminating lamp 42 which is energized by the power supply circuit 36and a light sensitive means or photosensitive cell 44 which are mountedin the developer unit 14 spaced from each other so that the light fromthe source 36 impinges on the light responsive means 44 by transmissionthrough or reflection from the developer liquid 18. In one construction,the elements 42 and 44 are immersed in the body of developer liquid 18in the tank 16. In another embodiment, the elements 42 and 44 aredisposed in proximity to a transparent or light transmitting portion orsection 24A of the outlet line 24 through which developer fluid isdischarged from the pump 20 to the applicator structure 26. Since thelight reflecting and transmitting characteristics of the developerliquid 18 vary in dependence on the quantity of toner or developerpowder in the liquid carrier, the incident light striking the lightresponsive means 44 varies in accordance therewith. The light responsivemeans 44 can be such that the resistance of this element decreases withincreasing illumination.

The light responsive element 44 is connected in series with a variableresistance element 46 across the output of the power supply circuit 36to provide a voltage divider connected to the base of a transistor 48,the collector of which is connected to the power supply circuit 36through a resistance element 50. The emitter electrode of thetransistor- 48 is returned to a reference potential, and the collectorelectrode is also coupled to a timing capacitor S2 through a seriesconnected resistance element 54. The point of common connection of thecapacitor 52 and resistance element 54 is connected to the emitter of aunijunction transistor 56. The power supply circuit 36 is of aconventional design and provides a well regulated constant voltageoutput to avoid the introduction of erroneous readings resulting fromvoltage uctuations.

The value of the variable resistance 46 is so adjusted that when thelight responsive means 44 receives a quantity of illuminationcorresponding to a correct level of toner material in the developerliquid, the bias applied to the base of the transistor 48 by the networkincluding the elements 44 and 46 maintains the transistor 48 in aconductive condition. By adjusting the value of the resistance 46, thecontrol circuit can be adjusted for operation with developer liquidshaving different ratios of developer material to carrier liquid.

The transistor 48 provides, in function, a switch for controlling theeffectiveness of a unijunction relaxation oscillator including theunijunction transistor 56. One base of the transistor 56 is connected tothe power supply circuit 36 through a resistance element 58, and theother base of the transistor 56 is connected to a source of referencepotential through the winding 34A of the relay 34, the winding beingshunted by an oppositely poled diode 60 to provide transientsuppression. In the normal condition of the control circuit 10, thetransistor 56 is in a nonconductive condition.

However, when the level of toner or developer material in the developerliquid 18 drops below a given level, the light responsive means 44receives greater illumination so that the effective resistance of thiselement drops. This reduces the positive bias applied to the base of thetransistor 48 so that this transistor is placed in a nonconductivecondition. The capacitor 52 then charges in series with the resistanceelements 50 and 54 until the point is reached at which a sucientlypositive bias is applied to the connected base of the unijunctiontransistor 56. At this time, the unijunction transistor 56 is placed ina conductive conditon to energize the winding 34A of the relay 34 sothat the contacts 34B are closed. If the delay interval of the timingdevice 38 has been completed, the solenoid 32 is energized.

When the unijunction transistor 56 is placed in a conductive condition,the very low impedance of the emitterlower base path permits thecapacitor 52 to discharge through the winding 34A so that the biasapplied to the emitter of the transistor 56 is reduced. When this biasis reduced to a given level, the unijunction transistor 56 is placed ina nonconductive condition to terminate the energization of the winding34A of the relay so that this relay releases to open the contacts 34Band thus release the solenoid 32. The operation and release of thesolenoid 32 discharges a predetermined quantity of developer concentrateinto the body of developer liquid 18 contained in the reservoir or tank16 and thus terminates the rst dispensing operation.

The termination of conduction through the transistor 56 also permits thecapacitor 52 to again |be charged over the series circuit including theresistance elements 50 and 54. When the capacitor 52 is again charged tothe point at which the emitter is biased sufficiently positive, thetransistor 56 is placed in operation to again operate the solenoid andto discharge the capacitor 52. This periodic operation and release ofthe solenoid 32 under the control of the relay 34 and the transistor 56continues so long as the transistor 48 is maintained in a nonconductivecondition. The value of the resistance element 54 can be varied toadjust the time interval between successive operations of the solenoid32.

When the level of toner material in the developer liquid 18 reaches thedesired level, the illumination of the cell 44 is reduced, and thevoltage dividing network including the elements 44 and 46 again biasesthe base of the transistor 48 suciently positive with respect to itsemitter so that this transistor is placed in a conductive condition.When the transistor 48 is placed in a conductive condition, a lowimpedance shunt is provided across the network including the capacitor52 and resistance element 54 and further charging of this capacitor andoperation of the relaxation oscillator including the transistor 56 isterminated. In this manner, the quantity of toner or ratio of toner tocarrier liquid in the developer unit 14 directly and automaticallycontrols the dispensing of developer material. A switch 62 providesmanually operated means for controlling the operation land release ofthe relay 34 and the solenoid 32.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. In a liquid developer unit of the type in which photoelectrostaticcopy material is contacted with a developer liquid containingparticulate developer material,

a detecting means for examining the developer liquid and providing anoutput signal varying in dependence on the composition of the developerliquid,

a dispensing unit for dispensing developer material to the liquiddeveloper unit and operable to dispense a predetermined amount ofdeveloper material in response to each operation of the dispensing unit,and

a control circuit connected between the dispensing unit and thedetecting means and controlled by the output signal, said controlcircuit including means for repetitively operating the dispensing unitat xed time intervals to automatically add a series of saidpredetermined amounts of developer material to the liquid developer unitfor so long as the composition of the developer liquid is not at apredetermined level, the control circuit being placed in operation whenthe composition of the developer liquid changes and remainingcontinuously operative to provide repetitive operation of the dispensingunit at said fixed time intervals until the developerliquid returns tothe predetermined level.

2. The liquid developer unit set forth in claim 1 in which the controlcircuit includes a time delay means for inhibiting operation of thedispensing unit under the control of the output signal for apredetermined time interval.

3. The liquid developer unit set forth in claim 1 in which the controlcircuit includes means for adjusting the xed time interval betweenoperations of the dispensing means.

4. In a liquid developer unit of the type in which photoelectrostaticcopy material is contacted with a developer liquid containingparticulate developer material,

a light source,

a light responsive means spaced from the light source to permit aportion of the developer liquid to be disposed therebetween, the lightresponsive means receiving a varying amount of light from the lightsource in dependence on the composition of the developer liquid andproviding a corresponding output,

a developer dispensing unit for dispensing developer material to theliquid developer unit,

a control circuit connected between the developer dispensing unit andthe light responsive means and controlled by the output of the lightresponsive means for operating the developer dispensing unit toautomatically add developer material to the liquid developer unitwhenever the composition of the developer liquid changes from apredetermined level,

pumping means for circulating the developer liquid in the developerunit,

mean for starting operation of the pumping means,

means for preventing operation of the dispensing unit for a period oftime following the starting of the pumping means and for thereafterautomatically rendering the dispensing unit responsive to control by thelight responsive means.

5. In a liquid developer unit of the type in which an electrostaticimage is developed by contact with the developer liquid containingparticulate developer material, the light transmitting characteristic ofthe developer l-iquid varying as the quantity of developer materialchanges,

a ligh-t source for illuminating the developer liquid,

light responsive means receiving light from the developer lightresulting from illumination of the developer liquid by the light source,the quantity of light varying in accordance with the developer materialin the developer liquid,

a developer dispensing unit for dispensing a predetermined quantity ofdeveloper material to the liquid developer unit in response to eachoperation of the dispensing unit,

a first control means connected to 4the dispensing unit for repetitivelyoperating the dispensing unit at fixed time lintervals to supply Iaseries of increments of said predetermined quantity of developermaterial to the liquid developer uni-t, and

a second control means conne-cted -to the first control means and thelight respon-sive means f-or placing the first control means in and outof operation in dependence on the light received from the developerliquid.

6. In a liquid developer uni-t of the type in which an electrostaticimage is developed by contact with a developer liquid containingparticulate developer material, the light transmitting characteristic ofthe developer liquid varying as the quantity of developer materialchanges,

a light source for illuminating the developer liquid,

light responsive mean-s receiving light from the devel-oper liquidresulting from illumination of the developer liquid by the light source,the quantity of light varying in accordance with lthe developer materialin lthe developer liquid,

developer -dispensing uni-t for dispensing developer material to theliquid developer unit,

first control circuit connected to the dispensing unit yand operablewhen rendered effective to intermittently operate the dispensing unit tosupply devel-oper material to the liquid developer unit and operablewhen rendered ineffective to inhibit operation of the dispensing unit,and

second control circuit connected to the first control circuit andincluding the light responsive means for rendering the first controlcircuit effective and ineffective to operate the dispensing unit independence on the light received by the light responsive means from thedeveloper liquid.

7. The liquid developer unit set forth in claim 6 including which thefirst control circuit includes a controlled conduction devicealternately operable to conductive and nonconductive states under thecontrol of a capacitive means. 9. The liquid developer unit set forth inclaim 8 including a potential source, and in which the second controlcircuit includes means controlled by the light responsive means forcontrolling the connection of the potential source to the capacitivemeans.

References Cited UNITED STATES PATENTS 2,956,487 10/1960 Giaimo.

3,094,049 6/ 1963 Snelling 118-637 XR 3,233,781 2/1966 GrubbS 222-573,361,113 1/1968 Hoffman et al. 118-637 3,369,524 2/1968 Fuhrer 118-6373,381,662 5/1968 Kolb et al 118-637 PETER FELDMAN, Primary Examiner U.S.Cl. XR.

